With the development of information processing technology, people are required to understand an unprecedented amount of information. Therefore, people seek technology that will efficiently extract information necessary for the people and eliminate unnecessary information. For instance, development of technology to extract necessary words from text in an input electronic document is advancing.
However, if only words are displayed, it is difficult to understand the contents. The importance of necessary words varies depending on users, types of documents, etc., and also changes with time, situation, etc. It is therefore difficult to maintain high levels of satisfaction for support.